(1) Field of the Invention
The present invention relates to a reception display apparatus for receiving data and displaying a screen based on the received data. More particularly, the present invention relates to a technique for receiving and using broadcast data which is provided in a plurality of layers.
(2) Description of Related Art
In recent broadcast-type data communications, an idea similar to the OSI (Open Systems Interconnection) reference model for two-way communications has been introduced. That is to say, in most of recent standards, the broadcast data is provided in a plurality of layers and a separate protocol is used for each layer. Here, the broadcast-type data communications refer to one-way data communications in which data is transmitted from a transmission side to a reception side.
FIG. 36 shows a process in which the transmission side generates data blocks in a plurality of lower layers from a data block in a higher layer.
As shown in FIG. 36, a data block α in the higher layer is divided into a plurality of pieces of data A, B, C, . . . The protocol information is attached to the front and rear of each piece of divided data. The protocol information and a piece of divided data constitute a data block in a lower layer. The protocol information includes at least information necessary for reconstructing a data block in a higher layer. The protocol information attached to the front of data is referred to as header; and the protocol information attached to the rear of data is referred to as footer.
FIG. 37 shows a process in which the reception side generates a data block in a higher layer from data blocks in a plurality of lower layers.
As shown in FIG. 37, a data block a in the higher layer is reconstructed from each data block in lower layers based on the protocol information, the header and the footer.
If data were not divided into a plurality of data blocks in a lower layer, all data would have to be received again when a reception error occurs to a part of the data. For example, image files such as a JPEG (Joint Photographic Experts Group) files have a large data size. When receiving such a large file in a poor reception condition, it may take a lot of time before the file is received completely or the file may not be received completely since reception errors often occur to different portions in the file each time the file is transmitted. However, when such a large file is transmitted and received as a plurality of data blocks in a lower layer, even if a reception error occurs, only the data block to which the reception error has occurred needs to be transmitted again. In this case, the re-transmitted data block has a rarer chance to have a reception error since its data size is small. Furthermore, it does not take much time to receive the re-transmitted data block. As a result, the number of failures in receiving files decreases, and the time taken for completely receiving such a large file is also reduced drastically.
However, when the broadcast data is provided in a plurality of layers, the data in the highest layer, that is to say, the data which is reproduced for use by the user cannot be reproduced until the data blocks in the lower layers are completely received. This is because the data in the highest layer is reconstructed from the data blocks in the lower layers, in order from the lowest layer. That is to say, even if almost all the data blocks in a layer second to the highest layer are reconstructed, the data in the highest layer cannot be used unless the data blocks in the lower layer are completely reconstructed and the data in the highest layer is reconstructed from the data blocks.
For example, in a data broadcast service with which the user can watch information such as a weather forecast or a TV program guide by tracing user files such as HTML (Hyper Text Markup Language) files linked in a tree structure, user files as boughs and leaves cannot be referred to when user files as the stem or the boughs of them cannot be reproduced. However, the possibility that the user reaches the desired information increases if information having been received normally can be reproduced immediately even if the received information is only a part of a whole piece of information to be received.